1. Field of the Invention
The present invention relates to an engine having an oil pump suitable for a small-sized vehicle, such as a motorcycle.
2. Description of Background Art
A known oil pump structure includes a relief path that is curved into an arc extending in a pump circumferential direction and a plate-like oil filter disposed in the relief path so as to traverse obliquely the relief path. See, for example, Japanese Utility Model Laid-Open No. Hei 2-34778. The oil filter is a mesh plate that is arcuately curved so as to follow along the relief path, thus offering a large filter area.
A variable flow rate oil pump is also known that includes a main pump unit and a sub-pump unit having different delivery rates from each other in order to increase or decrease the delivery rate of the oil pump according to an operating condition of an engine. The variable flow rate oil pump further includes, instead of a simple relief valve, a pressure regulating valve connected to the main pump unit and the sub-pump unit. The pressure regulating valve changes over a hydraulic path according to the applicable delivery rate. If the same type of mesh filter as in the related art is to be incorporated in the variable flow rate oil pump, a need arises to find a space for disposing the oil filter in a complicated oil path between each pump unit and the pressure regulating valve. More specifically, a need exists for a structure that allows the oil filter to be disposed efficiently in order to prevent the variable flow rate oil pump including the pressure regulating valve from becoming large in size as a result of disposing the oil filter.